1. Field of the Invention
The present invention relates to cutting devices having a positioning mechanism for positioning a cutting unit at a plurality of left or right tilt positions.
2. Description of the Related Art
Cutting devices are known that has a cutting unit vertically tiltable relative to a table for cutting a workpiece placed on a table. The cutting unit has a rotary cutting tool, such as a circular grinding wheel or a circular saw blade. The cutting unit is tiltable also laterally (left and right). A positioning mechanism is provided for positioning the cutting unit at a predetermined left or right tilt position.
Among the cutting devices, those used mainly for cutting wooden materials have a table rotatable within a horizontal plane. A cutting unit is supported on the table, so that the cutting unit rotates to change its direction within a horizontal plane as the table rotates. On the upper side of the table, a positioning fence is provided for positioning a workpiece within the horizontal plane. Therefore, rotating the table relative to the positioning fence can change a cut angle of a rotary cutting tool of the cutting unit relative to a reference surface of the workpiece. Therefore, by vertically pivoting the cutting unit, the rotary cutting tool can cut the workpiece in a direction inclined relative to the reference surface within a horizontal plane. This cutting operation is called an “oblique cutting operation” and during the oblique cutting operation, the rotational axis of the rotary cutting tool is held to extend horizontally. On the other hand, with the cutting unit tilted laterally in left or right direction, where the rotational axis of the rotary cutting tool is inclined relative to the horizontal plane, it is possible to cut a workpiece in a direction inclined relative to a vertical direction. This cutting operation is called an “inclined cutting operation.”
In order to enable the inclined cutting operation, it is necessary to position the cutting unit at a left or right tilt position in addition to a vertical position (where the cutting unit is not tilted laterally). To this end, various positioning mechanisms have been proposed, for example, in U.S. Pat. No. 7,337,702 and Japanese Laid-Open Patent Publication Nos. 2003-205501 and 2003-245901.
The positioning mechanisms of the above published documents are basically the same and each mainly includes a base portion (stationary side) fixed to the table and a support portion (tilting side) coupled to the base portion via a horizontal support shaft so as to be capable of rotating within a predetermined range about an axis of the support shaft. The cutting unit is supported on the support portion. Stopper bolts are mounted to one of the base portion and the support portion. Stopper projections are provided at the other of the base portion and the Support portion for abutment to the stopper bolts, so that the cutting unit can be positioned at any of the vertical position and the tilt position without need of observation of an angle scale. This type of positioning mechanism is called a “positive stop mechanism.”
However, the positioning mechanisms of the above publications still need improvements. For example, in the case of the positioning mechanism of U.S. Pat. No. 7,337,702, the cutting unit can be selectively positioned at a plurality of tilt positions in left or right direction by the operation of an operation rod. However, if a user forgets to return the operation rod to its original position after the inclined cutting operation has been performed with a large tilt angle, a workpiece may still be cut with the large tilt angle regardless of the user's intention to cut the workpiece with a smaller tilt angle after that. If this occurs, disposal of the workpiece as waste would be necessary. On the other hand, if a user forgets to return the operation rod to its original position after the inclined cutting operation has been performed with a small tilt angle, a workpiece may be cut with the small tilt angle regardless of the user's intention to cut the workpiece with a larger tilt angle after that. However, in this case, an additional cutting operation may be preformed to cut the workpiece at the large tilt angle.
Thus, in the case that the positioning mechanism allows the cutting unit to be selectively positioned at a plurality of tilt positions in left or right direction, forgetting the operation of the operational rod after the inclined cutting operation with a large tilt angle may lead to disposal of the workpiece as waste.
Therefore, there is a need in the art for a positioning device that is improved in operability for positioning a cutting unit of a table cutting device at a plurality of positions tilted in a left or right direction.